For general instructions on getting node polyfills for react-native, checkout parshap/node-libs-react-native on GitHub.

1. First you'll need to install a few dependencies:

• Install the @nuid/zk-react-native package instead of @nuid/zk. This is a react-native specific version of NuID's zk package (which has an identical JS interface to @nuid/zk).
• You'll also need react-native-randombytes as a top-level dependency in your app so that react-native will link it correctly.
• And finally, node-libs-react-native for shimming node dependencies in react-native which is necessary to support zk credential and proof generation.

$ yarn add @nuid/zk-react-native node-libs-react-native react-native-randombytes
# if RN < 0.60
$ react-native link react-native-randombytes
# else RN >= 0.60, instead do
$ cd iOS && pod install

2. Next, modify metro.config.js to add extraNodeModules configuration to wire up node-libs-react-native correctly:

// metro.config.js
module.exports = {
  // ...
  resolver: {
    extraNodeModules: require('node-libs-react-native')
  }
};

3. Import node-libs-react-native/globals before you import @nuid/zk-react-native:

// my-rn-project/index.js
// Add globals here (or anywhere _before_ importing @nuid/zk-react-native)
import 'node-libs-react-native/globals';
import { registerRootComponent } from 'expo';
import App from './src/app';
registerRootComponent(App);